Rotatable bi-planar series-fed log-periodic hf antenna

ABSTRACT

A unidirectional broadband horizontally polarized HF bi-planar rotatable log-periodic antenna with the radiating element to boom structure of each of the planar antenna half structures substantially the same and flipped 180* one from the other. The bi-planar antenna is series fed through the lower boom acting as an infinite balun with the center conductor connected across to the forward end of the upper boom. The two half structures are relatively closely spaced with a dielectric insulator providing mutual structural support between the upper and lower booms of the half structures, and a vertical conductive material mast joins the structural booms both electrically and mechanically. The radiating elements are relatively fat truncated triangular teeth in a foreshortened log-periodic antenna employing a relatively large Alpha angle of approximately 75*, a Tau ratio of approximately 0.5, and an array angle of Psi of less than approximately 10*.

United States Patent Cory et al.

1 51 Oct. 10,1972

[54] ROTATABLE BI-PLANAR SERIES-FED LOG-PERIODIC HF ANTENNA [72]Inventors: Terry S. Cory; Roger A. Markley,

both of Richardson, Tex.

[73] Assignee: Collins Radio Company, Dallas,

Tex.

[22] Filed: June 14, 1971 [211 App]. No.: 152,767

521 u.s.c| ..343/763,343/792.5 51 Int. Cl. ..l-l0lq 11/10 [58] Field ofSearch....343/763, 766, 792.5, 884, 90s

[56] References Cited UNITED STATES PATENTS 2,977,597 3/1961 Du Hamel etal ..343/792.5

Primary ExaminerEli Lieberman Attorney-Warren H. Kintzinger et al.

[57] ABSTRACT A unidirectional broadband horizontally polarized HFbi-planar rotatable log-periodic antenna with the radiating element toboom structure of each of the planar antenna half structuressubstantially the same and flipped 180 one from the other. The bi-planarantenna is series fed through the lower boom acting as an infinite balunwith the center conductor connected across to the forward end of theupper boom. The two half structures are relatively closely spaced with adielectric insulator providing mutual structural support between theupper and lower booms of the half structures, and a vertical conductivematerial mast joins the structural booms both electrically andmechanically. The radiating elements are relatively fat truncatedtriangular teeth in a foreshortened logperiodic antenna employing arelatively large 0: angle of approximately 75, a 1- ratio ofapproximately 0.5, and an array angle of I of less than approximately10.

9 Claims, 15 Drawing Figures PATENTEDncnoasrz v 3.697.999

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INVENTORS TERRY s ROGER A. MARK ATTORN Y PATENTEDnm 10 I972 SHEET 6 0F 6INVENTORS TERRY s. com ROGER A. MA KLEY F Wu l 1. I 6&1 I? ,3 9 0 9 93iv a x? 04 0 g a ROTATABLE BI-PLANAR SERIES-FED LOG- PERIODIC HF ANTENNAThis invention relates in general to antenna systems and, in particular,to rotatable bi-planar series-fed log periodic, unidirectional HFantennas of minimal turning radius size for a broadband range ofoperation (8-25 MHz for example).

While there have been many rotatable log periodic antennas designedparticularly for land-based use, there have been very few especiallydesigned for ships. Some antennas that have been designed for shipboarduse employ insulated dipole elements that are susceptible to vibrationdamage obviously an undesired state. Further, spatial limitations aresuch with many ships and some other installation environments thatattempts have been made to reduce the size of what were originallyland-based designs. One approach to antenna size reduction has been tomake use of lumped inductive loading techniques with these, however,reducing antenna efficiency and having a susceptibility to failure.

Projected shipboard usage dictates a conservative rugged design approachwith particular emphasis directed to effects of wind, ice, ships pitchand roll, vibration, shock and corrosion. Ships do encounter severestorms from time to time that antennas must be able to survive andthrough which they must be capable of providing reliable service. Allstructural connections in the antenna structure must be exceptionallyclean so that contamination-collecting pockets are eliminated.Dissimilar metal connections should be held to a minimum and pottedtoexclude moisture particularly with the salt entrained humid airencountered at sea to minimize or prevent corrosion. Further, it isimportant that the antennas be structurally tight clean designs withpredominately metal to metal interconnect in an electricallyall-grounded antenna assembly that may be painted with atightly-adhering epoxy-polyamide primer and glossy white acrylic topcoat or their protective equivalents.

It is, therefore, a principal object of this invention to provide aunidirectional broadband horizontally polarized HF bi-planar rotatablelog-periodic antenna of foreshortened minimum size for an antennaoperational through approximately a frequency band of from 8 MHz to 25MHz.

Another object is to provide such antennas of reduced size havingminimal turning radius requirements without making use of lumpedinductive loading techniques.

A further object is to provide such antennas with a structurally tightclean design with predominately metal-to-metal interconnect in anelectrically allgrounded" antenna assembly.

Features of the invention useful in accomplishing the above objectsinclude, in a unidirectional broadband horizontally polarized HFbi-planar rotatable logperiodic antenna, a frequency band of from 8 MHzto approximately 25 MHz in an antenna with a maximum turning radius ofapproximately 28 feet. It is a foreshortened antenna with a goodfront-to-back ratio of at least 10 db down from the peak of the mainbeam throughout the frequency range of operation. The antenna is acontinuously rotatable antenna having a coaxial feed system that extendsthrough the mast and the interior of the lower boom to the front of theantenna as a series feed with the lower boom acting as an infinite balunand the center conductor connected across to the forward end of theupper boom. The antenna structure and mast assembly are substantially anallmetal all-grounded structure with only a dielectric insulatorproviding mutual structural support between the forward ends of theupper and lower booms of relatively closely spaced half structures ofthe antenna. The antenna half structures are substantially identicalplanar log-periodic radiating element structures flipped 180 one fromthe other. The radiating elements in each half structure are relativelyflat truncated triangular teeth in a foreshortened log-periodic antennaemploying a relatively large at angle of 75 for each half structure, a1' ratio of 0.5 and a half structure array 1' angle of 7.

A specific embodiment representing what is presently regarded as thebest mode of carrying out the invention is illustrated in theaccompanying drawings.

- rotatable bi-planar log-periodic I-IF antennas;

FIG. 2, a horizontal plan view of the bi-planar antenna of FIG. 1;

FIG. 3, a side elevation view of the antenna of FIG. 1;

FIG. 4, a perspective view of another rotatable antenna embodimentsimilar in many respects to the antenna of FIG. 1;

FIG. 5, a horizontal plan view of the bi-planar antenna of FIG. 4;

FIG. 6, a side elevation view of the antenna of FIG. 4;

FIG. 7, a partial enlarged rotatable antenna mast and feed detail;

FIG. 8, a partial upper and lower boom front end dielectric structureand feed interconnect detail;

FIG. 9, a VSWR to frequency in MHz diagram for both antennas; I

FIG. 10, 11 and 12, II-plane patterns for the antennas at 8 MHz, 15 MHz,and 24 MHz respectively; and

FIGS. 13, 14 and 15, azimuth E-plane voltage patterns for the antenna at8 MHz, l5 MHz and 24 MHz respectively.

Referring to the drawings:

The rotatable unidirectional broadband horizontallypolarized HFbi-planar log-periodic antenna 20 of FIGS. 1, 2 and 3 is shown to haveplanar upper and lower half structures 21 and 22 respectively that aresubstantially the same but flipped one from the other. These two halfstructures 21 and 22 are stacked vertically and arrayed with respect tocommon apex at a 1' angle of approximately 7 in the bi-planar antennastructure that is rotatable about the vertical center line of rotatableantenna mounting shaft 23. The longitudinally extended upper and lowerboom structures 24U and 24L, respectively, may be in the form of steppedtubular fabricated construction, as shown, or tapered tubes, not shown,with the larger portions thereof at the large rear lower frequency endof the antenna to the smaller high frequency apex end of the antenna.The upper and lower booms or longerons 24U and 24L are structurallyinterconnected by a vertical conductive material mast such as metal tube25 that may be in line with rotatable antenna mast 23, as shown, orlongitudinally displaced therefrom if desired. A dielectric insulator 26provides mutual structural support between the forward ends of the upperand lower booms 24U and 24L. Antenna rotatable mounting detail and boomforward end dielectric insulator and antenna feed detail is shown ingreater detail in FIGS. 7 and 8, hereinafter described in more detail,not only for the embodiment of FIGS. 1, 2 and 3 but also for theembodiments of FIGS. 4, 5 and 6. In any event, the bi-planar antenna isseries-fed through the lower boom acting as an infinite balun with thecenter conductor 27 connected across the forward end of insulator spacer26 to the forward end of upper boom 24U.

The upper boom 24U mounts first a single monopole type conductive metalextension 28U extended at a forward angle from one side of the forwardportion of boom 28U. An inline extension is continued on the other sidethereof as a forward structural tubular or rod extension 29U of atruncated triangular tooth relatively fat radiating element 30U with theends of both radiating structural elements 28U and 29U and the rearextension 31U of the tooth 30U terminated at a relatively large a angleof 75. Conductive structural element 29U in axial alignment with theelement 28U of the other side are slanted relative to boom 24U so thatwith tooth 30U rear radiating element conductive metal tube or rodextension MD is slanted approximately the same amount, in the oppositedirection, relative to the boom 24U, a triangular truncated tooth isformed. The outer ends of radiating element structural rods 29U and 31Uare interconnected by rod 32U, or conductive cable in place thereof, toform a relatively fat triangular truncated tooth radiating element 30U.

The opposite side rod extension 33U in axial alignment with rod 31U isthe forward slanted member of truncated triangular tooth 34U- having arear element extension 35U that is slanted in the opposite direction ofextension SSH and the outer ends of extensions 33U and 35U areinterconnected by conductive interconnect member 36U. It is of interestto note that the successively larger truncated tooth extension membersstarting with rod extension 35U are formed with en- 7 larged innerportions such as tubular portion 37U and that all of the successivelylarger lower frequency radiating element extensions are equipped withsuch structural strengthening sections. The upper half section is inlike manner equipped with the successively larger fat radiating elementtruncated triangular teeth 38U, 39U and 40U in alternate side-to-siderelationship with the final triangular largest low frequency triangulartruncatedtooth 40U having a rear extension 41U axially in line with amonopole type extension 42U to the opposite side that is provided with aformed over tip and 43U a little within the limits of the 75 a angle.The tip end 43U lets the radiating element effective length be effectiveat the lowest designed operational frequency while in cooperation withformed over tip end 43U permitting a relatively small antenna turningradius of 28.3 feet for a foreshortened antenna having an operationalfrequencyrange of 8 MHz to 25 MHz.

The lower antenna half structure 22 is in effect the flip mirror imageof the upper antenna half structure 21 with the effectively fatradiating element truncated triangular teeth thereof in line with thetooth gaps of the upper half structure and the teeth of the upper halfstructure in line with the gaps of the lower half structure. This iswith the triangular truncated tooth outer end truncated conductivemembers lying along the respective at angle sides with the teeth in eachhalf structure being progressively larger in log-periodic relation inaccord with a 1' ratio of 0.5 and in this structure with a halfstructure 1' angle of 7. The upper and lower half structures of theantenna are relatively closely spaced so as to effectively electricallybe quasi coplanar and the 1' angle could actually fall in a range offrom approximately 10 down to approaching 0 with the half structuresoriented toward an infinitely spaced forward apex without adverselyeffecting or varying the performance of the antenna structure. Therotatable mast 23 of the'embodiment of FIGS. 1, 2 and 3 and for thatmatter of the embodiment of FIGS. 4, 5 and 6 is mounted on a stubsupport mast 44. Nonconductive dielectric rope tension members 45U, 46U,47U, 480 and 49U in the upper half structure and 45L, 46L, 47L, 48L and49L in the lower half structure advantageously enhance structuralintegrity of the antenna unit particularly in dampening radiatingelement vibrations.

Referring now to the rotatable log-periodic antenna embodiment of FIGS.4, 5 and 6, the smaller radiating element and teeth are the same as withthe embodiment of FIGS. 1, 2 and 3, except that dielectric tensionmembers such as those employed with the embodiment of FIGS. 1, 2 and 3are not used. Teeth and radiating elements otherwise duplicating thoseof the FIG. 1, 2 and 3 embodiment carrying the same numbers and portionssimilar carrying primed numbers as the case may be. The major differenceof this embodiment resides in the lowest frequency larger rear radiatingelements being much shorter rear end radiating element members in orderthat an antenna having the same operational frequency range of 8 MHz to25 MHz as with the embodiment of FIG. 1 be attained in a minimum sizeantenna with a turning radius as small as 23.7 feet. This antennaprovides substantially the same advantageous operational capabilities asthose attained with the embodiment of FIGS. 1, 2 and 3 and has the sameat angle, 1' ratio of 0.5 and upper and lower half structure array Iangle of 7. While the largest rear element transverse length in theembodiment of FIG. 1 is slightly less than a half wavelength at thelowest frequency of 8 MHz by virtue of the formed over conductive ends43U and 43L, the FIGS. 4, 5 and 6 embodiment is considerably furtherforeshortened in the transverse dimension at the expense of slightlygreater cost in order to ensure mechanical ruggedness of the folded backrear elements. With this approach rearward most triangular truncatedteeth 40U and 40L are formed with a bent over inwardly extended ends 50Uand 50L, respectively, extending from forward turned corner 51U and 51Llying on the at angle limit lines and also on the inscribed turningradius circle of 23.7 feet. End members 50U and 50L extend as cords of acircle to tip ends 52U and 52L that contact the inscribed tuming radiuscircle at a material distance to the rear of connective junction withthe transverse rear tooth projection rod structures 41U and 41J. Theopposite side rear projections in axial alignment projections 42U' and42L in longitudinal alignment with the projections 40U and 41L extend tocomers 53U and 53L respectively at the turning radius inscribed circleto extend forwardly therefrom in radiating element ends 43U' and 43Lthat are materially longer than their counterparts 43U and 43L of theembodiment of FIG. 1.

Referring also to FIG. 7 the shipboard fixed stub support mast 44includes an RF coaxial connection to radio equipment via line 55 thatconnects to rotary joint means in an azimuth rotator and coaxial RFrotary joint unit 56. Coaxial line 52 extends up rotary shaft 23 to theinterior of lower boom 24L within which the grounded outer sheath coaxline 57 extends to the forward end (see FIG. 8) with the forward centerconductor 27 thereof being passed through a dielectric nonconductive.boom 24L end cap 58 to lie across the dielectric material member 26 toelectrically connected connection with the end of boom 24U. The azimuthrotator and coaxial RF rotary joint unit 56 is driven by a drive motor59 structurally mounted along with the unit 56 on the mast 44, that isalso equipped with an access plate 60. The structural dielectric member26 that interconnects the forward apex end of booms 24U and 24L is fixedin place in assembly with the forward end of the booms by strap and boltassemblies 61. It should be noted that the internal mast and lower boom24L coaxial line 57 internal feed to the forward end of the lower boom24L acts as an infinite balun feed to the antenna structure and includesthe inner coaxial line lead 27 cross connection to the forward end ofthe upper boom 24U forward end. This advantageously functions very wellin a substantially all electrically grounded antenna structure with feedfrom the forward end of the structure being in effect inductivelytransmitted down the structure with the upper and lower half structuresin the bi-planar log-periodic structure being quasi-planar operationallyto and thereby enhance inductive feed the forward apex end to theresonant element area of the antenna throughout the frequency range ofoperation thereof. This is particularly enhanced with the optimizedtriangular truncated tooth shape with a combination between trapezoidalfatness near the element ends and tapering of the elements to providesome spacing between adjacent teeth as the half structures are broughtclose together. With this structure the feed exciting wave progressestoward the longer elements from the feed tip end is guided from elementto element in this inductive action along the entire antennalongitudinal length. This is evidenced by the ability to place a shortcircuit along the booms in the vicinity of the geometric mean spacingbetween element tie-on points without the operation of the antennas.

The unidirectional broadband horizontally polarized HF bi-planarrotatable log-periodic antenna embodiments of FIGS. 1 and 4 have VSWR tofrequency in MHz characteristics that vary to some degree only in thelower 8 MHz to 12 MHz region. The portion thereof indicated by dottedline, representing a somewhat higher VSWR through that range, is for thesmaller turning radius embodiment of FIG. 4, and the VSWR to frequencycharacteristics for the larger tuming radius antenna embodiment of FIG.1 is shown in solid through the 8 MHz to 12 MHz region. Both antennashave duplicate VSWR to frequency in MHz operational characteristicsthroughout the remainder of their operational frequency range from 12MHz to 24 MHz. The elevation H-plane patterns for the antennas areadvantageously quite good as shown for 8 MHz, 15 MHz and 24 MHz in FIGS.10, 11 and 12, respectively. Furthermore, the E-plane patterns remainvery much the same through the frequency range of operation in theantenna such as is the case with the patterns for 8 MHz, 15 MHz and 24MHz as shown by FIGS. l3, l4 and 15, respectively.

Whereas this invention is herein illustrated and described with respectto a specific embodiment thereof, it should be realized that variouschanges may be made without departing from the essential contributionsto the art made by the teachings hereof.

We claim:

1. In a unidirectional broadband horizontally polarized HF bi-planarrotatable log-periodic antenna, operational through a substantiveportion of an 8 MHz to 24 MHz frequency range; upper and lower antennaplanar half structures substantially the same and flipped 180 one fromthe other; said half structures each having a relatively large 0: angleapproximating in a foreshortened antenna structure with a 1' ratio ofapproximately 0.5 and with a I angle between half structuresin the arraytoward a common apex of less than approximately 10.

2. The unidirectional broadband rotatable logperiodic antenna of claim1, wherein each of said upper and lower half structures includes aplurality of truncated triangular teeth alternating opposite sides; andwith truncated triangular tooth outer edges lying substantially alongrespective a angle limit lines.

3. The unidirectional broadband rotatable logperiodic antenna of claim2, wherein the antenna is provided with a coaxial line feed system; saidupper and lower half structures each include a longitudinally front torear extended center boom; and rotatable mounting of said antenna on amast structure.

4. The unidirectional broadband rotatable logperiodic antenna of claim3, wherein said mast structure includes a fixed mast portion; and arotatable portion mounted on said fixed mast portion.

' 5. The unidirectional broadband rotatable logperiodic antenna of claim4, wherein coaxial RF line feed means is extended through said fixedmast portions and said rotatable portion; and with a coaxial line feedsection extended through said lower half section boom from saidrotatable mast portion to the front end of the boom; and a coaxial linefeed section center line electrical feed cross connection to the forwardend of the upper half section boom.

6. The unidirectional broadband rotatable logperiodic antenna of claim5, wherein the forward ends of the upper and lower half section boomsare structurally interconnected by a dielectric material structuralmember; and with the booms interconnected by a conductive materialstructural member in the mast supporting area of the antenna structure.

7. The unidirectional broadband rotatable logperiodic antenna of claim6, wherein rearward mast lowest frequency radiating elements of saidhalf structures have bent over and inwardly angled electricallyconductive end extensions.

8. The unidirectional broadband rotatable logperiodic antenna of claim7, wherein said antenna inscribes a turning radius of approximately 28feet.

9. The unidirectional Broadband rotatable logperiodic antenna of claim7, wherein said antenna inscribes a turning radius of approximately 24feet.

* l II

1. In a unidirectional broadband horizontally polarized HF biplanarrotatable log-periodic antenna, operational through a substantiveportion of an 8 MHz to 24 MHz frequency range; upper and lower antennaplanar half structures substantially the same and flipped 180* one fromthe other; said half structures each having a relatively large Alphaangle approximating 75* in a foreshortened antenna structure with a Tauratio of approximately 0.5 and with a Psi angle between half structuresin the array toward a common apex of less than approximately 10*.
 2. Theunidirectional broadband rotatable log-periodic antenna of cLaim 1,wherein each of said upper and lower half structures includes aplurality of truncated triangular teeth alternating opposite sides; andwith truncated triangular tooth outer edges lying substantially alongrespective Alpha angle limit lines.
 3. The unidirectional broadbandrotatable log-periodic antenna of claim 2, wherein the antenna isprovided with a coaxial line feed system; said upper and lower halfstructures each include a longitudinally front to rear extended centerboom; and rotatable mounting of said antenna on a mast structure.
 4. Theunidirectional broadband rotatable log-periodic antenna of claim 3,wherein said mast structure includes a fixed mast portion; and arotatable portion mounted on said fixed mast portion.
 5. Theunidirectional broadband rotatable log-periodic antenna of claim 4,wherein coaxial RF line feed means is extended through said fixed mastportions and said rotatable portion; and with a coaxial line feedsection extended through said lower half section boom from saidrotatable mast portion to the front end of the boom; and a coaxial linefeed section center line electrical feed cross connection to the forwardend of the upper half section boom.
 6. The unidirectional broadbandrotatable log-periodic antenna of claim 5, wherein the forward ends ofthe upper and lower half section booms are structurally interconnectedby a dielectric material structural member; and with the boomsinterconnected by a conductive material structural member in the mastsupporting area of the antenna structure.
 7. The unidirectionalbroadband rotatable log-periodic antenna of claim 6, wherein rearwardmast lowest frequency radiating elements of said half structures havebent over and inwardly angled electrically conductive end extensions. 8.The unidirectional broadband rotatable log-periodic antenna of claim 7,wherein said antenna inscribes a turning radius of approximately 28feet.
 9. The unidirectional broadband rotatable log-periodic antenna ofclaim 7, wherein said antenna inscribes a turning radius ofapproximately 24 feet.